[1.28.0] ClassLength (and cops that rely on CodeLengthCalculator) crash on methods without parens

[Darhazer]

The changes in #10543 introduced a crash, when the send node omits parenthesis

---

Spec to reproduce:

      it 'counts single line correctly if asked folding' do
        source = parse_source(<<~RUBY)
          def test
            foo foo: :bar, baz: :quux
          end
        RUBY

        length = described_class.new(source.ast, source, foldable_types: %i[hash]).calculate
        expect(length).to eq(1)
      end

Expected behavior

Spec to pass

Actual behavior

     Failure/Error: parent.loc.begin.end_pos != descendant.loc.expression.begin_pos,
     
     NoMethodError:
       undefined method `end_pos' for nil:NilClass
     # ./lib/rubocop/cop/metrics/utils/code_length_calculator.rb:162:in `omit_length'